1. Field of the Invention
The invention relates to an internal combustion engine knock control apparatus and method for making a knock determination based on an output signal from a knock sensor and changing an engine control amount based on the determination results.
2. Description of the Related Art
As is well known, in many internal combustion engines, knock control is performed in which a knock determination is made to determine the presence or absence of knock and the ignition timing and the like is adjusted in accordance with the determination results. Ordinarily, the knock determination is made using a knock sensor, which is a vibration detecting sensor mounted on the cylinder block or the like. The presence or absence of knock is then detected based on an output signal from the knock sensor during a predetermined period (i.e., a knock determination period) after ignition in each cylinder.
Recently in-cylinder internal combustion engines, which have a fuel injector provided such that the nozzle hole is exposed to the combustion chamber, and in which fuel is injected directly into the cylinder, have been put into practical use. Some in-cylinder internal combustion engines can switch combustion systems, changing between homogeneous combustion and stratified-charged combustion, by changing the fuel injection timing between the intake stroke and the compression stroke based on the operating state of the engine. Other in-cylinder internal combustion engines improve the combustion state within the cylinders by controlling the airflow in each cylinder with an airflow control valve provided in the intake port or the like.
When the combustion mode of the internal combustion engine is changed by switching the combustion system or using airflow control or the like, the rate of combustion inside the cylinder changes which also changes the timing of knock occurrence after the fuel is ignited. In response to this, JP-A-10-159642 proposes technology which changes the knock determination period according to the combustion mode in an in-cylinder internal combustion engine. This technology enables suitable knock detection to be performed irrespective of a change in the timing of knock occurrence, which occurs when the combustion mode changes.
The fuel injector that injects the fuel in the internal combustion engine is designed such that, to start a fuel injection, an electromagnetic solenoid is energized to drive a nozzle needle away from a valve seat, thus opening a valve. To stop the fuel injection, the electromagnetic solenoid is de-energized such that the nozzle needle comes to be seated back against the valve seat.
When operated, this kind of fuel injector produces vibration, such as of a sound produced by the nozzle needle hitting the valve seat when the valve closes. This vibration may ride as noise on the output signal from the knock sensor. In particular, there is a tendency for the effect from the noise produced by operation of the fuel injector on the output signal from the knock sensor to be greater with in-cylinder injection type internal combustion engines than with port injection type internal combustion engines due to the fact that in in-cylinder injection type internal combustion engines the fuel injector is mounted nearer the knock sensor.
Conventionally, however, the knock determination period and the fuel injection timing were set without consideration given to the effect of the operational noise from the fuel injector on the knock determination. Therefore, it is possible that the operational noise from the fuel injector may ride on the output signal from the knock sensor during the knock determination period, which may result in an erroneous determination that knock is occurring even if, in actuality, it is not. As a result, improper control may end up being performed.
That is, when the knock determination period does not overlap with the fuel injection period, operational noise from the fuel injector does not ride on the detection signal from the knock sensor so background noise appearing on the detection signal is relatively low. In this case, when the fuel injection timing is switched so that the knock determination period overlaps with the fuel injection period, operational noise from the fuel injector starts to ride on the detection signal from the knock sensor. Immediately after this switch in the fuel injection timing, a knock determination is made presuming the background noise level that was low up until that point. Therefore, until the background noise level that reflects the correct operational noise from the fuel injector is learned, the operational noise from the fuel injector that appears on the detection signal from the knock sensor may be erroneously determined to be from knock. Then based on that erroneous determination, improper control in which an engine control amount, such as the ignition timing, is changed inappropriately ends up being performed.